Thermally responsive impedance unit



i 0 6 8 4 CROSS REFERENCE Oct. 17, 1950 L A. MEDLAR THERMAL-LYRESPONSIVE IIPEDANCE UNIT Filed Jan. 1o. 195o Patented Oct. 17, 1950UNITED STATES PATENT OFFICEI l THERMAILY msrjlirsslvn IMPEDANCE v i ILewis A. Media', oreiand, Pa., minier u Fox Products Company,Philadelphia. Pa., a corporation of Pennsylvania Application January 10,1950, Serial No. 137,804'

This invention relates to thermally responsive impedance units. and moreparticularly to thermistor units adapted to be inserted through thefilling opening of a storage battery to detect the internal temperatureof the battery. The present application is a continuation in part of.application Serial Number 87,494, filed April 14, 1949, by Lewis A.Medlar and James B. Godshalk.

As disposed in that applicaiton, battery chargers may be automaticallycontrolled. in response to the internal temperature of the battery beingcharged, by employing a thermistor subjected to the internal temperatureof the battery to regulate a relay circuit arranged to make and breakthe charging circuit in response to changes in resistance of thethermistor. In such a device, the relay or control circuit is locatedwithin the main casing of the battery charger, and the thermistor isconnected to the control circuit by means of an insulated cable. so thatthe thermistor may be inserted through the filling opening of a batterywhich is somewhat removed from` the charger casing. The thermistor mustbe protected from mechanical shock by a suitable casing secured to theend of the cable, and it is to the combination of thermistor, cable andcasing that the present invention specically relates.

An object of the invention is to devise a thermally responsiveresistance unit constructed for insertion through a storage batteryfilling opening and providing optimum transfer of heat to the thermallyresponsive resistance.

A further object of the invention is to provide a thermally responsiveunit comprising a rodlike thermistor of relatively small diameter, and anovel protective casing arrangement therefor, wherein the thermistor isso arranged as to be capable of withstanding severe mechanical shocks.

A still further object of the invention is to provide a thermallyresponsive unit comprising a rod-like thermistor electrically connectedto the conductors of a two-conductor cable and secured within a.protective casing, said casing having a novel configuration speciallyadapting the unit for ease of assembly.

Yet another object of the invention is to devise a thermally responsiveresistance unit constructed for insertion through a storage batteryfilling opening and providing for optimum transfer of heat from theinterior of the battery to the thermally responsive resistance butminimizing the effect upon the resistance of the temperature conditionoutside of the battery casing;

In order that the foregoing and other novel if e Claims. (Cl. 20L-63)features of the invention may be readily understood, reference is had tothe accompanying drawings forming a part of this specication and inwhich: A

Fig. 1 is a longitudinal section through a ther` mally responsiveresistance unit constructed in accordance with one embodiment oftheinvention, parts thereof being shown in elevation;

Fig. 2 is a longitudinal section through a 'thermally responsiveresistance unit constructed in accordance with a second embodiment ofthe invention, parts thereofbeing shown in elevation;

Fig. 3 is a view partly in side elevation and partly in longitudinalsection,I showing the device of Fig. 2 with the parts separated,illustrating the manner in which the device is assembled, and

Fig. 4 is a longitudinal section through a thermally responsiveresistance unit similar to that shown in Fig. 2, but including anexterior sheath of insulating material.

Referring now to the drawings, and-first to Fig. 1 thereof, it will beseen that the embodiment of the invention shown in this gure lncludes agenerally rod-like thermistor l, a tu'- bular casing 2 and atwo-conductor flexible electric cable 3. The cable I includes conductorsl and 5 and a relatively thick insulating sheath i, the insulatingsheath being trimmed well back from the ends of the conductors t and 5,and the conductors being bared and staggered for connection to thethermistor l. Conductor l is soldered to one end of the thermistor I at1, and conductor 5 is soldered to the opposite end of the thermistor at8, the cable thusv being adapted for connecting the thermistor Ato asuitable relay control circuit, as is fully described in the afore-'mentioned application, Serial No. 87,494.

The casing 2, which is of good heat conducting material, consists of atubular portion 9 and a closed end i0 which is substantially thickerthan the wall of the main portion 9. The open end of the casing 2 issecured over the end of the insulating sheath 6 'of cable 3, and thisconv nection is made fluid-tight, as by crimping the wall of the casingat] i. The length of the casing 2 is such that, when the casing issecured to the cable, the thermistor I extends close to the relativelythick end wall I0 of the casing. An insulating sleeve I2 covers thebared portion of conductor 5 and most of the length of thermistor l. Aninsulating tube i3 is provided to prevent contact between the exposedportion of thermistor l and the casing 2, and this insulating tubepreferably extends romthe end of the insulat- 3 ing sheath B of cable 2to the end wall I0 of casing 2.V

It will be seen that, in this embodiment of the invention, thethermistor I is supported substantially entirely by the conductors 4 and5 and is completely insulated electrically from the rcasing 2. Thethermistor is preferably of that general type prepared by molding andfiring mixtures of semi-conductive oxides of such metals as manganese,nickel, cobalt and copper, usually with a binder such as sodiumsilicate.

The casing 2, which preferably is made of leadplated bronze, is soproportioned that its diameter is cons*derably smaller than the fillingopening of a standard storage battery. When the unit is inserted throughthe battery filling opening. a portion of the casing, including therelatively thick end I thereof, will be in contact with the batteryelectrolyte, and the temperature of the electrolyte can thus readily besensed by the thermistor I because of the good heat conducting pathprovided by the end wall I0. Snce the cable 2, in actual practice,extends freely-from the main casing of the battery charger t'becontrolled by the thermstor, the thermistor unit is subjected torelatively severe mechanical shocks during movement of the charger. But,since the thermistor is supported substantially entirely by the wires 4and 5, such shocks are taken up by the wires.

A sond embodment of the invention is illustrated in Fig. 2, and againincludes a generally vrodli'te thermstor 2|, a tubular casing 22and aflexible cable 23 comprising conductors 24 and 2l and a relatively thickinsulating sheath 26. The casing 22 is provided with a central borecomprising a porton 28 of a diameter slightly larger than the outsidediameter of the thermistor 2|. a porton 21 oi' a diameter substantiallylarger than that of the portion 28, and a tapered portion 29 connectingthe portions 21 and 2l. The thermistor 2| is located within portion 22of the bore and is positioned wth its end even with end 2| of Ithecasing. The thermistor is supported substantially concentrlcally withinthe bore of the casing and is connected to the casing at the end 20 ol'the thermistor by a solder Joint 22. The opposite end of the thermistoris connected to conductor of cable 22, and a tube 22 of insulatingmaterlal is provided between the thermistor and portion 28 of the boreof the easing. this insulating t"be extending over most of the length ofthe thermistor.

The conductor 24 terminates in a bared portion 24a bent back over theinsulating sheath 26 of cable 22. Portion 21 of the bore of casing 22 ispositioned over the end of the cable 22, so that the bared portion 24aof conductor 24 is disposed between the outer surface of the insulatingsheath 26 and the inner surface of the casing. The wall of the casing iscrimped, as at 24, this crimping serving the dual functions of4 makingthe joint between the casing and the cable fluid-tight and assuring goodelectrical contact between the bared portion 24a of conductor 24 and thecasing.

ASince the solder joint 22 seals the opposite end of the tubular casing,entrance of fluid to the interior of the casing is prevented. Thethermistor unit just described provides a continuous electrical pathcomprising conductor 2l, thermistor 2|, solder joint 22, casing 22,which lis again preferably made from lead plated bronze,

and conductor 24. The thermistor 2| may thus vbe connected to a suitablerelay control circuit by the two conductors of cable 22, as is fully de-CII scribed in the aforementioned application, Serial Number 87, 494.

Fig. 3 illustrates the manner in which the structure Just described isadapted for assembly with a minimum of manual operations. The outerinsulation of cable 22 is ilrst stripped down to free the end ofconductors 24 and 2l, which are then bared for a distance as shown. Oneend of thermistor 2| is then soldered to the end of conductor 2l, andinsulating sleeve 22 is slipped into place to cover a major part of thelength of the thermistor and also the bared portion of conductor 25.Bared portion 24a of conductor 24 is bent over the outer insulation ofthe cable as shown. The resulting thermistor assembly is then insertedinto casing 22 via the larger portion 21 of the bore, and taperedportion 29 of the casing bore guides the thermistor into properposition. Solder joint 22, Fig. 2, is then made, and the casing iscrimped at 24 to cable 22, thus assuring contact between portion 24a ofconductor 24 and casipg 22, and completing the assembly.

'I'he provison of adequate transfer of heat from the batteryelectrolyte, when the unit just described is inserted in a storagebattery, is of particular importance since there is a tendency for heatto be conducted away from the thermistor by conductors 24 and 2l. Inthis connection, it will be noted that the end 2B of the thermistor isexposed for direct contact with the battery electrolyte. Further, thethermistor is positioned immediately adjacent the relatively thickerportion of the casing 22, and heat collected by this portion of thecasing is readily transferred to the thermistor by the solder Joint 22..As will be clear from Fig. 4, hereinafter described, when the unit isinserted in the battery, both the end 2| of the casing and the end 20 ofthe thermistor are in direct contact with the battery electrolyte. Thus,heat from the electrolyte is transferred to the thermistor both bydirect contact and through the relatively thick end portion ofthecasing. Further, when the unit is so inserted in the 4 battery, thecasing and the thermistor are in electrical contact with theelectrolyte, so that the circuit comprising conductors 24 and 25 isconnected to the electrolyte. Therefore, the unit can be employed withbattery charger safety circuits of the type disclosed in co-pendingapplication, Serial Number 97,772, flied June 8, 1949, by Lewis A.Medlar, now Patent 2,499,663.

The two embodiments of the invention shown in Fiss. l-3 and justdescribed appear in the aforementioned application, Serial Number87,494. I have found that, when the units shown in Figs. 1-3 vare usedin actual practice to control a battery charger, it is highly desirableto provide some means for reducing heat transfer between the thermallyresponsive resistance unit and the air surrounding the storage batteryin which the unit is inserted. When the thermally responsive units areemployed to control a battery charger, it is necessary that thethermistor be substantially at the temperature of the electrolyte of thebattery being charged. If the air surrounding the battery is at a lowtemperature. there is a decided tendency for heat to be conducted awayfromthe thermistor by the casing, since the casing usually extends abovethe top of the battery.

I therefore provide a continuous sheath of heat-insulating materialcompletely covering the casing, except for the tip thereof. Fig. 4illustrates the unit previously described with reference to Fig. 2, withsuch a sheath applied thereto. Here, it will be seen that the sheath 35ex'- tends from a point 36 on the cable 23 continu@ ously along theouter surface of the casing 22 for most of its length. The sheath 35 maybe of any suitable insulating material and may be applied in variousconventional manners well known in the art. I find it expedient toemploy as the sheath 35 a tube of vinyl plastic and to apply the tube tothe unit by shrinking the tube over the casing and cable, so that theresulting sheath follows closely the contour of the unit. as shown.

The material of the sheath 35, in addition to having sufllcient heatinsulating properties, should of course be sufilciently resistant tochemical attack by the battery electrolyte. Typical examples of suitablematerials for the sheath include such vinyl plastics as thevinyl-chloride aeetates, the vinyl chlorides, the vinyl-butyl resins,the polyethylenes, the chlorinated rubbers, synthetic and naturalrubbers, and similar materials.

In Fife. 4, the dotted lines at C and E indicate the positions of thebattery cover and electrolyte, respectively, relative to the unit whenthe unit is inserted in the battery. It will thus be seen that, whileheat may flow directly from the electrolyte to the thermistor, presenceof the sheath 35 prevents loss of heat along the casing to the airoutside of the battery. The tip of the casing,

indicated at 22, will normally be completely covered by the batteryelectrolyte, as shown, when the unit is in place in the battery.

In the embodiment of the invention shown in Fig. 2, I prefer to employas the thermistor element 2i a molded and red rod-like body ofsemi-conductive metal oxides, as in the case of thermistor element I,Fig. 1. Such thermistors are well known in the art and are particularlywell adapted for battery charger control applications because of theirresistance characteristics and high mechanical strength.

While the embodiment of the invention illustrated in Fig. 1 isadvantageous in that the thermistor clement, being supported out ofcontact with the casing by means of conductors 4 and 5, is resilientlymounted, this embodiment can not be used where it is necessary to bringthe thermistor into direct contact with the battery electrolyte. I havefound that the strucure shown in Fig, 2, wherein the termistor elementis secured at one end directly to the casing by means of a relativelymassive solder joint and is brought into direct contact with theelectrolyte when the unit is inserted in the battery, also providesgreat resistance to mechanical shock. Though, in this latter embodimentof the invention, mechanical shocks applied to the casing arenecessari'y transmitted directly to the thermistor element, the elementis rigidly supported at one end and, since the element is relativelyshort, the end thereof connected to conductor 25 is not liable to anyserious mechanical displacement. Also, it is preferable that theinsulating sleeve 33 which surrounds the free end of the thermistorelement be of suilicient thickness to substantially illl the spacebetween the thermistor element and the inner wall of the casing.

I claim:

1. A thermally sensitive resistance unit adapted to be subjected to theinternal temperature of a. storage battery by being inserted through afilling opening in the battery casing, comprising an electrical cableincluding two conductors and bore therethrough, one end of said casingbeing,

secured in iluid tight relation over an end of Said insulating sheath,and a generally rod-like thermally sensitive resistance elementpositioned in Y the bore of said casing and having one end electricallyconnected to said casing by a solder joint,

said solder joint closing said bore to prevent entrance of liquid, oneof said conductors being connected to the remaining end of saidresistance element, and the other of said conductors being connected tosaid casing.

2. A thermally responsive resistance unit adapted to be subjected to theinternal tempera.- ture oi' a storage battery by being inserted througha filling opening in the battery casing, comprising an electrical cableincluding two conductors and a. relatively thick in-,ulating sheath, agenerally rod-like thermally responsive resistance element, and a.tubular casing having a. bore therethrough, said casing comprising aportion of relatively large internal diameter at one end and a portionof relatively smaller internal diameter at the opposite end, saidresistance element being positioned within and closely spaced from thoportion of said casing of smaller internal diameter, one end of saidresistance element being electrically connected to said casing by asolder Joint, said lsolder joint closing said bore to the entrance ofliquid, the remaining end of said resistance element being connected toone conductor of said cable, the other conductor of said cable beingbared for a portion of its length and being bent back so as to extendalong the outer surface of said sheath, and said casing being tightlysecured, at the end thereof removed from said solder Joint, over the endof said sheath and the bared portion of said second conductor extendingalong the outer surface of said sheath.

3. A thermally responsive resistance unit comprising an electrical cableincluding two conductors and a relatively thick insulating sheath, anelectrically conductive tubular casing, and a. rod-like thermallyresponsive resistance element; sad casing havinar a bore including aportion of relatively large internal diameter at one end, a portion oi'relatively smaller internal diameter at the opposite end, and a taperedportion connecting said large and smaller portions; said resistanceelement having a diameter less than the internal diameter of the smallerportion of said bore and being located concentrically within saidsmaller portion of said bore with one end of said element flush with theend of said casing, said resistance element being supported within andelectrically connected to said casing by a solder joint at one end ofsaid resistance element said solder joint completely sealing the spacebetween said element and said casing against entrance of liquid; theother end of said resistance element being connected to one of theconductors of said cable; the other conductor oi' said cable being benthack to extend along the outer surface of the insulating sheath of saidcable, and

the portion of said casing of larger internal diameter being tightlysecured over the insulating sheath of said cable with the said bent backconductor portion being held in electrical contact with the innersurface of said casing by said insulating sheath.

4. A thermally responsive resistance unit adapted to be subjected to theinternal temperature of a storage battery by being inserted through afilling opening in the battery casing, compris ing an electrical cableincluding two conductors and a relatively thick insulating sheath; agenerally tubular casing oi' good heat conductive material. saidgenerally tubular casing being secured over the insulating sheath oisaid cable and including a portion extending beyond the end of saidsheath and terminating in a tip closed against entrance of liquid; athermally responsive resistance element positioned withinsaid cas-` ingadjacent said tip, the two conductors o! said cable being electricallyconnected to opposite ends of said resistance element, and a continuousheat insulating sheath completely covering the connection between saidcasing and the sheath of said cable and extending substantially to thetip of said casing.

5. A thermally responsive resistance unit adapted to be subjected to theinternal temperature of a storage battery by being inserted through afilling opening in the battery casing, comprising an electrical cableincluding two conductors and a relatively vthick insulating sheath; agenerally tubular casing of good heat conductive material, said casingbeing secured over the insulating sheath of said cable and including aportion extending to a tip spaced from the end of said sheath; arod-like thermally responsive 8 resistance element positionedconcentrically within said casing and extending to the tip thereof: asolder Joint electrically connecting said resistance element to saidcasing at the end of said element located at the tip of said casing.said solder Joint sealing the space between said casing tip and saidresistance element against entrance o! liquid, one of said conductors oisaid cable being connected to the end oi said resistance elementopposite said solder Joint and the other of said conductors o! saidcable being electrically connected to said casing. and a heat insulatingsheath extending continuously from a point on the exterior surface ofsaid cable substantially to the tip of said casing.

LEWIS A. MEDLAR..

nsrmsNcI-:s crran The following references are oi' record in the iile o!this patent:

UNITED STATES PATENTS Number Name Date 2,102,030 Quereau Dec. 14, 19372,216,375 Hinter Oct. 1. 1940 2,321,846 Obermaier June 15, 19432,379,530 Lederer July 3, 1945

